This invention relates to a non-directional pneumatic agricultural tire for use on farm tractors and similar agricultural type vehicles. Tractor tires must have good vibration characteristics on and off the road while maintaining good traction or drawbar characteristics. Such tires must also provide for the removal of soil, mud, etc., during in-field use.
In the past, agricultural vehicles were horse drawn. With the introduction of motorized tractors in the early 1900""s, the farm wheels were made of steel with traction cleats extending across the steel wheel. E. J. Farkas in 1922 patented a detachable tread for tractor wheels. U.S. Pat. No. 1,423,519 describes a rubber tread member that could be added to the steel cleat thus making it possible to cross a road without destroying the paved surface. These historical vehicles were greatly underpowered for the task of farming. Accordingly, the wheels were generally designed to be somewhat, if not entirely, non-directional with cleats inclined or normal to the direction of travel. The non-directional characteristic was helpful when the tractor became stuck In such cases, horses would be hooked to the rear of the vehicle and the tractor with the assistance of added horsepower could reverse itself out of the muck.
As tractor motors improved, the tires became directional in design. The tractor""s primary function required forward pulling power and tires were accordingly designed to enhance this feature.
In November 1995, U.S. Pat. No. 5,464,050 issued to Mark Leonard Bonko describing a novel non-directional tread having a set of at least three lugs having substantially parallel lug centerlines oriented at about 45xc2x0 and lug centers that lie along a substantially straight line across the tread edges.
This tire had lugs of substantially equal lengths and were relatively short when compared to the long bar lugs of the prior art directional tractor tires. The advantage of short lug lengths was greatly improved flexibility resulting in less soil compaction.
While the use of many short lugs has many beneficial features particularly dry traction performance, such a tire has room for improvement.
In particular the tire disclosed in the Bonko patent was best suited for four or more rows of lugs to avoid a low speed lug induced vibration that was evidenced when only three lugs rows were employed. The reason such a phenomena was occurred was related to the fact that as the tire rolled at certain axial locations only the center lug supported the load. On a hard road-like surface at high tire inflation, this makes the tire xe2x80x9cduck walkxe2x80x9d a term commonly referred to in the tire art. To avoid these phenomena it is desirable to have at least two lugs always contacting the ground in any axial path of the tires contact patch perpendicular to the direction of tire rotation. The Bonko patent requiring the lug centerlines to be parallel prevented or at least greatly limited the three-row lug pattern from achieving this result while still maintaining the open space between lugs for good wet traction. For that reason, Bonko choose a four-row lug pattern as his preferred tire.
That non-directional tire had excellent dry traction with acceptable wet traction. The farmer was very pleased with the ability to have good forward and reverse directional pulling power.
One perceived drawback of the design was that the tire looked slightly unbalanced and that under severe pulling or pushing loads, the tractor may see a sideways slippage. Bonko noted in his earlier patent that a mirror image tire could be made to create offsetting lateral forces to eliminate this concern, if needed. His test data showed an added cost of having both left side and right side tire molds was unnecessary. Nevertheless, to some farmers how the tire looks establishes how the tire will perform. Farmers, maybe more than any other group of tire buyers, are actually as a group very sophisticated and quite adept at understanding how mechanical devices work. They have an on the job engineering sense about them and they tend to network They communicate about what works and what is just a gimmick. They tend to want improved products, but they don""t want to risk their livelihood on products that even hint that they don""t work. Thus to gain wide acceptance of a new product, the engineers must make a product that looks like it will do the job. The challenge here was to develop a tire that has both actual and perceived advantages.
In DE 89 07 334U discloses an eastmover tire having the features described in the preamble of claim 1.
Bonko in this next generation of non-directional tires set out to increase the lug lengths and open the tread pattern by going to three rows of lugs. The resultant design had to avoid the xe2x80x9cduck walkxe2x80x9d phenomena, look aggressive and be directional, and provide superior mud traction and at the same time increasing the uniformity of tread wear over his predecessor non-directional tire. The inventive tire described below has exceeded all of the above mentioned design requirements and in very novel way.
A non-directional pneumatic agricultural tire (20) having a maximum section width (W), an axis of rotation, an equatorial plane perpendicular to the axis, a casing having a carcass (21) reinforced with rubber coated cord, a rubber tread (32) disposed radially outwardly of the carcass is disclosed.
The tread (32) includes an inner tread and a plurality of tread lugs (50A,50B,50C), the lugs respectively have a surface (58) with a length (ll) and a width (lw) defined as the distance between a first edge (52) and a second edge (54) wherein the length (ll) is at least three times the width (lw) and the length (ll) of the lugs (50A,50B,50C) are respectively at least 20% of the maximum section width (W).
Each lug has a centerline (63) defined by a line bisecting the lug surface along the length of the lug.
The tread (32) has a first and a second tread edge (33A,33B) and a net-to-gross ratio, the net-to-gross ratio being defined as the ratio of the surface area of the normally loaded and normally inflated tire tread rubber that makes contact with a hard, flat surface, divided by the area of the tread (32), including non-contacting portions such as grooves as measured around the entire circumference of the tire.
The tread (32) has sets (60) of three lugs, each set having two lugs being shoulder lugs (50A and 50B) having substantially parallel centerlines (63) and one central lug (50C) having a centerline (63) substantially perpendicular to the centerlines (63) of the shoulder lugs (50A,50B). The set (60) is repeated a plurality of times circumferentially about the tread (32). The set (60) extends along a line (63) through the lug centers (61) in a substantially straight line across the tread (32) from the first tread edge (33A) to the second tread edge (33B). The line (62) passing approximately through the center (61) of each lug of a set (60) forms an acute angle xcex8c with the equatorial plane of about 45xc2x0or more.
The tread (32) is characterized by a net-to-gross ratio of 30% or less, preferably 20% or less wherein the lugs (50A,50B,50C) have a ratio of the lug width (lw) to lug radial height (1h) being less than two-thirds over 70% of the lug length (ll) and the lug (50A) are circumferentially offset relative to the lugs (50B) by a distance X as measured between axial lines (90) tangent to an end (51) of lug (50A) and an axial line (92) tangent to end (51) of lug (50B), X being a circumferential distance of less than the width of the lugs (lw) and wherein the set (60) is oriented such that the axially inner ends (51) of lugs (50A) when extended by the dashed lines to end (53) of lug (50C) creates an asymmetric chevron (70) having an apex (73) and lug (50B) has an end (51) when extended by dashed lines to the end (51) of lug (50C) forms an asymmetric chevron (72) having an apex (74) lying primarily on an opposite tread half and oriented in an opposite direction than the chevron (73).
Each lug centerline (63) of the lugs (50A,50B,50C) are approximated by a line intersecting midway through, thus bisecting halfway between the first edge (52) and the second edge (54) of each lug, the centerline (63) extending parallel to the edges (52) and (54) of each lug. Definitions
xe2x80x9cAspect ratioxe2x80x9d of the tire means the ratio of its section height (SH) to its section width (SW) multiplied by 100% for expression as a percentage.
xe2x80x9cAxialxe2x80x9d and xe2x80x9caxiallyxe2x80x9d means lines or directions that are parallel to the axis of rotation of the tire.
xe2x80x9cBeadxe2x80x9d means that part of the tire comprising an annular tensile member wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes toe guards and chaffers, to fit the design rim.
xe2x80x9cBelt reinforcing structurexe2x80x9d means at least two layers of plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having both left and right cord angles in the range from 17 degrees to 27 degrees with respect to the equatorial plane of the tire.
xe2x80x9cCarcassxe2x80x9d means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads.
xe2x80x9cCircumferentialxe2x80x9d means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.
xe2x80x9cDesign rimxe2x80x9d means a rim having a specified configuration and width. For the purposes of this specification, the design rim and design rim width is as specified by the industry standards in effect in the location in which the tire is made. For example, in the United States, the design rims are as specified by the Tire and Rim Association. In Europe, the rims are as specified in the European Tyre and Rim Technical Organizationxe2x80x94Standards Manual and the term design rim means the same as the standard measurement rims. In Japan, the standard organization is The Japan Automobile Tire Manufacturer""s Association.
xe2x80x9cDesign rim widthxe2x80x9d is the specific commercially available rim width assigned to each tire size and typically is between 75% and 90% of the specific tire""s section width.
xe2x80x9cEquatorial plane (EP)xe2x80x9d means the plane perpendicular to the tire""s axis of rotation and passing through the center of its tread.
xe2x80x9cFootprintxe2x80x9d means the contact patch or area of contact of the tire tread with a flat surface at zero speed and under normal load and pressure.
xe2x80x9cInnerxe2x80x9d means toward the inside of the tire and xe2x80x9couterxe2x80x9d means toward its exterior.
xe2x80x9cLateral edgexe2x80x9d means the axially outermost edge of the tread as defined by a plane parallel to the equatorial plane and intersecting the outer ends of the axially outermost traction lugs at the radial height of the inner tread surface.
xe2x80x9cLeadingxe2x80x9d refers to a portion or part of the tread that contacts the ground first, with respect to a series of such parts or portions, during rotation of the tire in the direction of travel.
xe2x80x9cNet-to-gross ratioxe2x80x9d means the ratio of the normally loaded and normally inflated tire tread rubber that makes contact with a hard flat surface, divided by the area of the tread, including non-contacting portions such as grooves as measured around the entire circumference of the tire.
xe2x80x9cNormal inflation pressurexe2x80x9d refers to the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.
xe2x80x9cNormal loadxe2x80x9d refers to the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.
xe2x80x9cRadialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d means directions radially toward or away from the axis of rotation of the tire.
xe2x80x9cRadial-ply tirexe2x80x9d means a belted or circumferentially restricted pneumatic tire in which the ply cords, which extend from bead to bead are laid at cord angles between 65xc2x0 and 900 with respect to the equatorial plane of the tire.
xe2x80x9cSection heightxe2x80x9d (SH) means the radial distance from the nominal rim diameter to the outer diameter of the tire at its equatorial plane.
xe2x80x9cSection widthxe2x80x9d (SW) means the maximum linear distance parallel to the axis of the tire and between the exterior of its sidewalls when and after it has been inflated at normal pressure for 24 hours, but unloaded, excluding elevations of the sidewalls due to labeling, decoration or protective bands.
xe2x80x9cTire design loadxe2x80x9d is the base or reference load assigned to a tire at a specific inflation pressure and service condition: other load-pressure relationships applicable to the tire are based upon that base or reference.
xe2x80x9cTrailingxe2x80x9d refers to a portion or part of the tread that contacts the ground last, with respect to a series of such parts or portions during rotation of the tire in the direction of travel.
xe2x80x9cTread arc widthxe2x80x9d (TAW) means the width of an arc having its center located on the plane (EP) and which substantially coincides with the radially outermost surfaces of the various traction elements (lugs, blocks, buttons, ribs, etc.) across the lateral or axial width of the tread portions of a tire when the tire is mounted upon its designated rim and inflated to its specified inflation pressure but not subjected to any load.
xe2x80x9cTread width,xe2x80x9d means the arc length of the tread surface in the axial direction, that is, in a plane passing through the axis of rotation of the tire.
xe2x80x9cUnit tread pressure,xe2x80x9d means the radial load borne per unit area (square centimeter or square inch) of the tread surface when that area is in the footprint of the normally inflated and normally loaded tire.